diff --git a/2021/aoc/aoc.go b/2021/aoc/aoc.go
index 69fa93a..a35d4fc 100644
--- a/2021/aoc/aoc.go
+++ b/2021/aoc/aoc.go
@@ -2,6 +2,7 @@ package aoc
 
 import (
 	"bufio"
+	"fmt"
 	"io"
 	"io/fs"
 	"os"
@@ -103,3 +104,9 @@ func Ints(text string) (ns []int) {
 func ExLines(text string) []string {
 	return strings.Split(strings.TrimSpace(text), "\n")
 }
+
+func MustScan(text, format string, dests ...interface{}) {
+	if _, err := fmt.Sscanf(text, format, dests...); err != nil {
+		panic(err)
+	}
+}
diff --git a/2021/day19/main.go b/2021/day19/main.go
new file mode 100644
index 0000000..3f6e610
--- /dev/null
+++ b/2021/day19/main.go
@@ -0,0 +1,244 @@
+package main
+
+import (
+	"fmt"
+	"log"
+	"sort"
+	"strings"
+
+	"github.com/jdkaplan/advent-of-code/aoc"
+)
+
+func init() {
+	log.SetFlags(0)
+}
+
+func main() {
+	text := aoc.Input().ReadFile("day19.txt")
+	fmt.Println(part1(text))
+}
+
+func part1(text string) int {
+	scanners := parseInput(text)
+
+	offsets := make(map[int]Offset)
+	offsets[0] = Offset{tx: V{0, 0, 0}, rot: noRot}
+
+solve:
+	for len(offsets) < len(scanners) {
+		log.Println("Solved", len(offsets), "/", len(scanners))
+		for _, s2 := range scanners {
+			if _, ok := offsets[s2.id]; ok {
+				// Already solved
+				continue
+			}
+
+			for id, o1 := range offsets {
+				s1 := scanners[id]
+				tx2, r2, ok := match(s1, s2, 12)
+				if ok {
+					offsets[s2.id] = Offset{
+						tx:  tx2.rot(o1.rot).plus(o1.tx),
+						rot: rrot(o1.rot, r2),
+					}
+					continue solve
+				}
+			}
+		}
+	}
+	return uniqPoints(scanners, offsets)
+}
+
+type Offset struct {
+	tx  V
+	rot R
+}
+
+func uniqPoints(scanners map[int]Scanner, offsets map[int]Offset) int {
+	uniq := make(map[V]struct{})
+	for _, s := range scanners {
+		o := offsets[s.id]
+		for p := range s.readings {
+			u := p.rot(o.rot).plus(o.tx)
+			uniq[u] = struct{}{}
+		}
+	}
+	var ps []V
+	for p := range uniq {
+		ps = append(ps, p)
+	}
+	sort.Slice(ps, func(i, j int) bool {
+		pi, pj := ps[i], ps[j]
+		if pi.x != pj.x {
+			return pi.x < pj.x
+		}
+		if pi.y != pj.y {
+			return pi.y < pj.y
+		}
+		if pi.z != pj.z {
+			return pi.z < pj.z
+		}
+		return false
+	})
+	return len(uniq)
+}
+
+func parseInput(text string) (scanners map[int]Scanner) {
+	scanners = make(map[int]Scanner)
+	for _, block := range strings.Split(text, "\n\n") {
+		lines := strings.Split(block, "\n")
+
+		var id int
+		aoc.MustScan(lines[0], "--- scanner %d ---", &id)
+
+		readings := make(map[V]struct{})
+		for _, line := range lines[1:] {
+			nums := strings.Split(line, ",")
+			x := aoc.MustInt(nums[0])
+			y := aoc.MustInt(nums[1])
+			z := aoc.MustInt(nums[2])
+			readings[V{x, y, z}] = struct{}{}
+		}
+
+		scanners[id] = Scanner{id, readings}
+	}
+	return
+}
+
+func match(s1, s2 Scanner, req int) (translation V, rotation R, ok bool) {
+	for a1 := range s1.readings {
+		for a2 := range s2.readings {
+			for _, rot := range uniqRot {
+				tx := a1.minus(a2.rot(rot))
+
+				var matches int
+				for p2 := range s2.readings {
+					p1 := p2.rot(rot).plus(tx)
+					if _, ok := s1.readings[p1]; ok {
+						matches++
+					}
+				}
+
+				if matches >= req {
+					return tx, rot, true
+				}
+			}
+		}
+	}
+	return V{}, R{}, false
+}
+
+type Scanner struct {
+	id       int
+	readings map[V]struct{}
+}
+
+type V struct{ x, y, z int }
+
+func (v V) plus(u V) V {
+	return V{v.x + u.x, v.y + u.y, v.z + u.z}
+}
+
+func (v V) minus(u V) V {
+	return V{v.x - u.x, v.y - u.y, v.z - u.z}
+}
+
+func (v V) dot(u V) int {
+	return v.x*u.x + v.y*u.y + v.z*u.z
+}
+
+func (v V) rot(r R) V {
+	return rot(r, v)
+}
+
+type R struct {
+	xx, xy, xz int
+	yx, yy, yz int
+	zx, zy, zz int
+}
+
+func rot(r R, v V) V {
+	x := r.xx*v.x + r.xy*v.y + r.xz*v.z
+	y := r.yx*v.x + r.yy*v.y + r.yz*v.z
+	z := r.zx*v.x + r.zy*v.y + r.zz*v.z
+	return V{x, y, z}
+}
+
+func rrot(r1, r2 R) R {
+	rx := V{r1.xx, r1.xy, r1.xz}
+	ry := V{r1.yx, r1.yy, r1.yz}
+	rz := V{r1.zx, r1.zy, r1.zz}
+
+	cx := V{r2.xx, r2.yx, r2.zx}
+	cy := V{r2.xy, r2.yy, r2.zy}
+	cz := V{r2.xz, r2.yz, r2.zz}
+
+	return R{
+		rx.dot(cx), rx.dot(cy), rx.dot(cz),
+		ry.dot(cx), ry.dot(cy), ry.dot(cz),
+		rz.dot(cx), rz.dot(cy), rz.dot(cz),
+	}
+}
+
+var uniqRot []R = genUniqRot()
+
+var noRot = R{
+	1, 0, 0,
+	0, 1, 0,
+	0, 0, 1,
+}
+
+func genUniqRot() []R {
+	id := R{
+		1, 0, 0,
+		0, 1, 0,
+		0, 0, 1,
+	}
+	rx := R{
+		1, 0, 0,
+		0, 0, -1,
+		0, 1, 0,
+	}
+	ry := R{
+		0, 0, 1,
+		0, 1, 0,
+		-1, 0, 0,
+	}
+	rz := R{
+		0, -1, 0,
+		1, 0, 0,
+		0, 0, 1,
+	}
+
+	uniq := make(map[R]struct{})
+
+	push := func(ops ...R) {
+		r := id
+		for _, op := range ops {
+			r = rrot(op, r)
+		}
+		uniq[r] = struct{}{}
+	}
+
+	rotations := []R{rx, ry, rz}
+
+	push()
+	for _, r1 := range rotations {
+		push(r1)
+		for _, r2 := range rotations {
+			push(r1, r2)
+			for _, r3 := range rotations {
+				push(r1, r2, r3)
+				for _, r4 := range rotations {
+					push(r1, r2, r3, r4)
+				}
+			}
+		}
+	}
+
+	var rs []R
+	for r := range uniq {
+		rs = append(rs, r)
+	}
+	return rs
+}